While conventional x-ray imagers only display contrast in density, X-ray imaging spectrometers (XIS) enable extrapolation of the elemental composition of the material being imaged, as well. Such information is useful in manufacturing and medical diagnostics. One key challenge in using XIS in these applications includes making detectors insensitive to the visible light. Silicon detectors are commonly used for imaging X-ray due to their availability and low-noise. However, because silicon is also sensitive to visible light, an optical blocking filter is required to make silicon detectors insensitive to the visible light. If a visible light signal gets through the blocking filter, it will interfere with spectroscopy. Conventional blocking filters are fragile and challenging to integrate into the XIS.
XIS have been used in astronomy for many years. Conventional optical blocking filters, such as the ones used on the Chandra X-ray Observatory, which is one of the three National Aeronautics and Space Administration (NASA) great observatories, are free-standing. They are extremely thin because they have to permit X-ray transmission. The fragility of the filters adds significant challenge to the integration of such filters into the spectrometer and adds cost to the instrument. For space applications, the cost increase is even higher as a complicated chamber must be built around the spectrometer to protect the filters from the launch vibrations. In addition, the performance of free-standing filters cannot be optimized because the mechanical support layer, which typically comprises 200-nm polymer layer, reduces transmission of x-rays.